The subject invention concerns a guide line which is intended for the various kinds of machine cloths used in the papermaking, cellulose and similar industries such as forming fabrics, press felts, dryer cloths and the like, and which line is disposed in the machine cloth across the direction of travel of the latter.
Papermaking machines generally consist of three sections, viz. the forming section, the press section and the dryer section. The formation of the pulp into a paper sheet is effected in the forming section on a forming fabric or between two forming fabrics. As a rule, the forming fabrics are textile fabrics woven from monofilament, multifilament or metal threads. In the press section, the majority of the moisture remaining in the paper web is removed by pressing when the paper web travels through a plurality of press nips. In each press nip a felt or wire travels in parallel with the paper web through the nips. The felt preferably is a textile base weave made from spun yarns or filament onto which a fibrous batt is needled. Press fabrics have a construction equal to that of forming fabrics, only coarser. In the dryer section, the paper web is dried to suitable moisture contents. The drying is effected through abutment of the paper web against heated dryer cylinders. The force of abutment of the paper web against the cylinder is increased with the aid of a dryer felt or dryer screen which serves to press the paper web against the cylinder. Both dryer felts and dryer screens are textile fabrics. The felt may consist of a base weave onto which a batt is needled or of a weave alone. The dryer screen generally is a multi-layered monofilament or multifilament weave. All machine cloths in a papermaking machine travel in endless condition over a number of rolls having varying functions. The endless condition is effected either by weaving the cloth endless or by interconnecting the cloth ends in the manufacture or in the installation of the cloth.
A machine cloth is a flexible unit in which the regular array of perpendicular lengthwise and crosswise threads may be distorted. When the distorsion surpasses a certain angle ridges or creases form in the lengthwise direction of the machine cloth. The travelling machine cloth has a certain lengthwise tension therein and since the cloth itself like the system of rolls incorporated in the travelling loop are not perfect, problems of guidance and control may arise as a result of the often considerable web travelling speeds of up to and above 1000 m/min. The machine cloth is guided by a roll or rolls in the system that may be positioned obliquely. Some machine cloth webs have an automatic system built into them so that in case the web is displaced and migrates too far to one side an edge sensing device is arranged to affect the operation of the guide roll.
Particularly in the case of press felts it is common practice to provide a guide line on the felt proper to allow the staff working on the papermaking machine to establish by visual inspection the manner in which the felt travels and to correct the felt orientation manually, should the felt bias on distortion have become too large. Woven press felts and press fabrics are provided with guide lines by introduction of a number of coloured threads into the weave. Application of guide lines in needled felts used to be made through painting but this method is both work-consuming and unsatisfactory. In latter years, subliming dyes have been used which are transferred by heat from a paper sheet onto the felt. This method, although an advantage from a technical and manufacturing point of view, at the same time has a negative effect on the durability of the guide line. This is particularly true in the case of felts comprising fibres of polyamides, since the subliming dyes cannot satisfactorily be chemically bonded to polyamide fibres. Particularly the wet strength of the guide line is unsatisfactory and sometimes the dye disappears rather quickly.
However, considerable problems are connected in establishing the shape and configuration of the guide line by visual inspection, when the felt travels at speeds in the neighbourhood of 1000 m/min. In addition, the felt soon becomes dirty and for this reason alone it may be impossible to see the line. Gradual distortion of the guide line is also difficult to register, particularly since the papermaking machine is in operation 24 hours a day and the staff is replaced continuously. Another disadvantage inherent in painted guide lines are the disturbances and vibrations that may be caused by the guide line.